This concerns a gel which combines many desirable properties with ease of manufacture. The gel is firm, cohesive and adhesive. It is stable at relatively high temperatures (80 degrees C.) as well as low temperatures (below 0 degrees C.); and it is a good electrical conductor. As a result, the gel makes a superior medical electrode. Because of its stability and low irritation potential, the gel may also be used for topical administration of drugs. Another application is in an improved room freshener.
The gel comprises:
a first polymer that dissolves, hydrates or disperses in hot water and that forms or can be made to form a rigid gel on cooling,
a hot water insoluble polymer that dissolves or hydrates on cooling and is compatible with said first polymer, and
water, said polymers having been combined in hot water.
For convenience, a polymer that dissolves, hydrates or disperses in hot water will be referred to herein as a hot water soluble polymer.
Preferably the hot water soluble polymer is kappa carrageenan; and the hot water insoluble polymer is hydroxypropylmethylcellulose (HPMC). Advantageously, the kappa carrageennan and HPMC are food grade products and the gel also contains common preservatives such as benzyl alcohol, methyl paraben, and propyl paraben. In some applications, it is desirable to use an electrolyte such as potassium chloride or potassium carbonate in this gel to increase its rigidity or conductivity. However, carrageenan itself is a relatively good conductor and the gel may be used as an electrode gel without the addition of a separate electrolyte.
If desired, glycerol, propylene glycol or other polyhydric alcohols may be used to reduce the rate of evaporation from the gel; and Locust bean gum, sodium carboxymethylcellulose, other compatible gums, sodium stearate, potassium stearate or other compatible soaps may be used to plasticize it. Surfactants such as the sodium linear alkylate sulfonates (e.g., Ultrawet DS) and the sodium linear alkylbenzene sulfonates (e.g., Sulframine 85) may be used with this gel to increase its adhesion.
Because a hot water soluble polymer is combined in hot water with a hot water insoluble polymer, a high proportion of the hot water insoluble polymer can be incorporated into the hot water soluble polymer at elevated temperatures without causing a prohibitive increase in the viscosity of the hot composition. Consequently, the gel can be manufactured rapidly in large quantities using only simple heating and stirring equipment.